T cell costimulation plays a vital role in coordinating both long- and short-term responsiveness of the adaptive immune system. An emerging picture of this process is that the spatial organization of costimulatory signaling complexes within the immune synapse has a major influence on subsequent cell activation. To directly test this concept, we introduced a system based on a planar substrate that presents multiple ligands to the T cell TCR, CD28, and LFA-1 receptors, thereby directing the organization of this artificial model of the immune synapse. With this platform we previously demonstrated that CD4+ T cells are sensitive to microscale changes in the organization of these signals, as measured by secretion of IL-2, and that mouse and human cells exhibit very different responses to these patterns. The proposed study seeks to use this platform to identify specific molecular processes that coordinate TCR and CD28 signaling, particularly with regards to how the spatial organization of these complexes influences this crosstalk. We also introduce the use of multicomponent supported lipid bilayer systems to explore the nanoscale organization of these interfaces. We focus specifically on PKC8 and Lck as two recognized molecules at the junction of these pathways, and seek to define how the biophysical behaviors of these proteins within the cell influence overall network function. We use the mouse and human cell models as two extreme examples of the overall response, in an effort to identify how the distribution, mobility, and directed motion of these molecules, in response to different organizations of TCR and CD28 signaling, influence traditional cell signaling concepts, such as phosphorylation. Successful completion of these studies will directly provide new insight into how PKC8 and Lck coordinate T cell costimulation. The methods we introduce are widely applicable, and will directly impact the study of signaling in a wide range of cellular systems.